Parameter Optimization of a Microfabricated Surface Acoustic Wave Sensor for Inert Gas Detection
- PDF / 1,534,401 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 3 Downloads / 218 Views
75 Mat. Res. Soc. Symp. Proc. Vol. 459 ©1997 Materials Research Society
conductivity of ZnO has been found to have a direct relationship with the presence of metastable atoms. Kupriyanov et al. [9, 10] employed activating thin-film surfaces with microcrystals of metals that interact with metastable atoms (thus demonstrating electron coupling with semiconductors) but the results did not demonstrate the direct correlation of a parametric change with He pressure. Much other work has been done using metastable He but none has reported the use of a microsensor that was fabricated specifically for detection of metastable He [11, 12]. Surface interaction in the gaseous phase is due primarily to the high density of metastable atoms, and a robust method of inert gas detection is available through metastable He detection. This paper discusses a micromachined SAW sensor that detects metastable He. The sensing system used in this device consists of an Au-activated TiO 2 film on an LiNbO 3 piezoelectric substrate. A method to deposit the TiO 2 film has also been proposed. The unique aspect of the present research is the development of a microsensor with the potential for detecting a frequency change of the SAW with respect to a variation in the electrical conductivity of an Au-activated TiO 2 thin film deposited on the delay line of the SAW microsensor when exposed to metastable He atoms. EXPERIMENT Figure 1 shows the configuration of the He SAW microsensor, which consists of(a) a sensing device that uses a pair of transmitting and receiving IDTs with a delay line coated with an Auactivated TiO 2 film capable of sensing metastable He and (b) a reference device configured in the same manner but without the sensing film on the delay line [13]. By comparing the outputs from the sensing and reference devices, we investigated the exposure and reactivity of the sensing film on the delay line to metastable He atoms. An Au-activated TiO 2 thin film was deposited by using an Edwards Auto 306 reactive electron beam evaporator. Reactive electron-beam evaporation was utilized in thin-film deposition because the metal transforms directly from vapor to solid and the thin films are rapidly cooled (=I1013 K/s), leading to ultrafine structures [14]. TiO 2 thin films are chemically resistant and have high temperature stability. Several researchers have studied different starting materials such as TiO 2, Ti 30 5, and TiO [15]. The present investigation was oriented toward utilizing Ti2 0 3 as a source material due to its uniform evaporation rate. Ti 20 3 has not been explored greatly in terms of surface roughness, and a successful attempt was made to deposit consistent-quality thin TiO 2 films by introducing 02 into the chamber. Oxygen chamber pressure was altered until good-quality TiO 2-rich films were produced. To begin the deposition, we placed the Ti 20 3 powder in an Mo crucible inside the evaporator. The background chamber pressure of 5 x 10-6 torr was used with a deposition rate of 0.2 nm/s. When Ti2 0 3 began evaporating and a stable d
Data Loading...
